Optical communications can use wavelength-division multiplexing (WDM) to transmit different channels of communication signals carried by optical carriers at different optical wavelengths through a single fiber or optical waveguide. To further increase the data carrying capacity of light at a single optical wavelength, polarization multiplexing based on two orthogonal optical polarizations at the same optical wavelength can be used to carry two different optical channels, one optical polarization per channel, hence doubling the capacity of the information carried at a particular optical wavelength.